Various processes and catalysts exist for the copolymerization of ethylene and alpha-olefins. For example, U.S. Pat. No. 3,113,115 discloses that a plastomeric copolymer of ethylene and propylene may be prepared using a catalyst system comprising diethyl aluminum chloride and titanium tetrachloride while U.S. Pat. No. 3,300,459 discloses that an elastomeric copolymer of ethylene and propylene containing from 20 to about 70 weight percent ethylene can be prepared using a catalyst system comprising trihexyl aluminum and vanadium oxychloride. From this technological base, processes for the production of the commercially important elastomeric ethylene-propylene copolymers, commonly referred to as EP elastomers, and the elastomeric terpolymers of ethylene, propylene and a nonconjugated diolefin, generally referred to as EPDM elastomers have been developed.
U.S. Pat. No. 3,166,517 discloses that a catalyst system prepared by reacting, in the presence of carbon tetrachloride or trichloromonofluoromethane, (a) aluminum triisobutyl, diisobutylaluminum chloride or isobutyl aluminum dichloride and the reaction product of 0.5 to 2 moles of aluminum chloride with 1 mol of aluminum triisobutyl, with (b) vanadium tris(acetylacetonate); the proportions of (a) and (b) being selected so that the value of the molar ratio of isobutyl radicals to vanadium atoms is at least 6:1, can be used for the production of EP and EPDM elastomers by polymerization of the appropriate monomers.
U.S. Pat. No. 3,767,630 discloses that high molecular weight copolymers of ethylene, propylene and 1,3-butadiene which are linear, unsaturated and amorphous can be prepared by a process wherein the aforementioned monomers are polymerized in the presence of an aromatic hydrocarbon using a catalytic system that comprises (a) at least one hydrocarbon soluble vanadium compound selected from the group consisting of vanadium halides, vanadium oxyhalides, vanadium acetylacetonates, vanadyl acetylacetonates, vanadyl halogenacetylacetonates, vanadium alcoholates and vanadyl halogen-alcoholates; (b) the product of the reaction between at least one dialkyl-aluminum monohalide having a linear or branched alkyl radical containing up to 16 carbon atoms and in which the halide is chlorine or bromine, and water, in a molar ratio of 2:1, and (c) at least one organic aluminum compound containing halogen, the ratio between the aluminum atoms of components (b)+(c) and the vanadium atoms of compound (a) being between 10:1 and 60:1 and the molar ratio between component (c) and component (b) being between 1:10 and 10:1.
The majority of the current EP and EPDM production processes are of the continuous type and the Ziegler-Natta catalysts used for the production of the high molecular weight elastomers are soluble catalysts formed from vanadium compounds such as vanadium tetrachloride, vanadium trisacetylacetonate, vanadium trialkoxides and halogenated vanadium alkoxides which are used singly or as mixtures in conjunction with an organoaluminum compound such as triethyl aluminum, diethyl aluminum chloride or ethyl aluminum sesquichloride. However, use of such catalyst systems are not without their problems as the processes are difficult to carry on for sustained periods.
There is a tendency for material to build up and adhere to the walls and to the agitation means of the reaction vessel containing the polymerization mixture thereby reducing the heat transfer capability of the equipment necessary for proper control of the reaction. Moreover, the mixing capability of the agitation means is altered, resulting in the homogeneous distribution of the species present in the reaction vessel being adversely affected.